Antibiotic use during pregnancy and neonatal Group B Streptococcus disease.

OBJECTIVES

To examine the association between prenatal antibiotic exposure and Group B Streptococcus (GBS) disease within 4 weeks postpartum.

METHODS

We conducted a population-based cohort study including all singleton live births in Sweden from 2006 to 2016, using national registers. Neonates were classified by prenatal antibiotic exposure status, and GBS disease was ascertained within four weeks postpartum. Adjusted odds ratios (aOR) were estimated using multivariable logistic regression with a robust variance estimator. Effect heterogeneity by GBS risk factors was evaluated, and potential confounding by indication was assessed by additional adjustment for these risk factors.

RESULTS

Among 1,095,644 liveborn singletons, 24.5% were exposed to antibiotics. GBS incidence was higher among exposed neonates than unexposed (0.86 vs. 0.66 per 1000 live births; aOR, 1.29; 95% CI, 1.10-1.50), particularly among neonates without GBS risk factors (aOR, 1.34; 95% CI, 1.12-1.60). The strongest association occurred with early third-trimester exposure (aOR, 1.67; 95% CI, 1.17-2.38). Associations for antibiotics given within four weeks of delivery attenuated after adjustment for GBS risk factors.

CONCLUSIONS

Prenatal antibiotic exposure can raise GBS risk within 4 weeks postpartum, especially in neonates not covered by risk-based intrapartum prophylaxis, with the early third-trimester being a critical window of susceptibility.